The present invention relates generally to combine harvesters and, more particularly, to improvements in their cleaning apparatus to permit a leveling thereof under side hill conditions.
Combines of the type concerned herein are large, self-propelled vehicles for cutting and threshing grain. A combine has a header which has a blade that will cut the crop. An auger mounted to the header delivers the crop up into a threshing chamber. The threshed grain falls onto a set of upper and lower sieves. The sieves separate the grain from the chaff, with the grain falling through the holes in the sieve into a collection area. Air is blown upward through the sieve holes so that the chaff is blown from the combine.
A combine works best while it is level. The grain is evenly distributed across the sieves while the sieves are level. However, a large percentage of the tillable acreage in the United States has hillside grades and terraces. Often it is necessary to cut the hillsides and terraces in back and forth sweeps, with the combine leaning laterally. When the combine leans, grain piles up on the downhill portions of the sieve and thus the grain is distributed onto the sieves unequally. This reduces the effectiveness of the separation between the chaff and the threshed grain. This uneven distribution of the grain on the sieves forces farmers to slow down so that the grain does not build up on the downhill side of the combine to the point where grain is lost from the combine.
Attempts to maintain combine sieves in a horizontal orientation while the combine is operating under side hill conditions can be found in several prior art patents. One such patent is U.S. Pat. No. 3,731,470. The apparatus disclosed in this patent provides a leveling of the entire frame of the combine through the operation of hydraulic cylinders to maintain the cleaning apparatus in a generally horizontal orientation. Since the entire combine is maintained in a level orientation, this patent teaches the modification of the connection of the crop harvesting header to the combine to permit a proper gathering of the crop material to be harvested. However, this mechanism is complicated and expensive to manufacture as well and cumbersome in operation.
Another prior art device that comprises a leveling sieve apparatus is described in U.S. Pat. No. 5,282,771. This patent discloses a plurality of sieve sections that pivot on their longitudinal axis so that their top surface always remains level relative to the horizon. The sieve sections are pivoted by an electronic motor that senses the lateral inclination of the combine through an electronic sensing means called an inclinometer. The problem with the device described in this patent is that the electronic sensing means and the electric motors that pivot the sieve sections are expensive to install and to operate. Furthermore, there is usually a lag time between the inclinometer sensing the lateral inclination of the combine, and the actual pivoting of the sieve sections. This lag time can lead to inefficient separating of grain.
Yet another prior art device that discloses efficient grain separation in a combine is described in U.S. Pat. No. 2,310,610. This patent teaches a method wherein a moveable deflector plate is combined with a pendulum to direct falling grain away from the downhill side of the combine's sieves. Although this device may direct falling grain to the uphill side of the sieves, the device is inefficient because once the grain falls onto the sieves, gravity will pull it to the downhill side of the combine, resulting in grain buildup on the downhill side.
U.S. Pat. Nos. 2,893,558 and 3,108,064 each describe a device which employs a screw-type auger traversing the sieve plate. When grain accumulates at the downhill side of the sieve, the screw-type auger pushes the accumulated grain toward the center of the sieve. The problem with these devices is that the collected grain is directed toward the center of the sieve rather than toward the high edge of the sieve, and therefore these devices only take advantage of half of the sieve's surface area.
Therefore there is a need for a leveling sieve mechanism that is cost effective and efficient in that it uses the entire surface area of the sieve to separate the grain.